Identification of a two-component signal transduction system involved in fimbriation of Porphyromonas gingivalis

Research progress on two-component signal transduction systems in Porphyromonas gingivalis

Porphyromonas gingivalis (P. gingivalis), a Gram-negative oral anaerobe, is considered to be a major pathogenic agent involved in the onset and progression of chronic periodontitis. P. gingivalis must be able to perceive and respond to the complicated changes in host to survive the environmental challenges, in which the two-component signal transduction systems (TCSs) play critical roles by connecting input signals to cellular physiological output. Canonical TCS consists of a sensor histidine kinase and a cognate response regulator that functions via a phosphorylation cascade. In this review, the roles of TCSs in P. gingivalis were demonstrated by illustrating the target genes and modulation modes, which may help elucidate the underlying mechanisms in future studies.

Phylogenetic diversity in fim and mfa gene clusters between Porphyromonas gingivalis and Porphyromonas gulae, as a potential cause of host specificity

Background

Periodontopathic bacteria Porphyromonas gingivalis in humans and Porphyromonas gulae in animals are phylogenetically close and commonly have FimA and Mfa1 fimbriae. However, little is known about how fimA and mfa1 are phylogenetically different between P. gingivalis and P. gulae. Here, we examined phylogenetic diversity in their fim and mfa gene clusters.

Methods

Twenty P. gulae strains were isolated from the periodontal pocket of 20 dogs. For their genomic information, along with 64 P. gingivalis and 11 P. gulae genomes, phylogenetic relationship between the genotypes of fimA and mfa1 was examined. Variability of amino acid sequences was examined in the three-dimensional structure of FimA. The distance between strains was calculated for fim and mfa genes.

Results

Some fimA genotypes in P. gulae were close to particular types in P. gingivalis. Two types of mfa1 were classified as 70-kDa and 53-kDa protein-coding mfa1. The variable amino acid positions were primarily at the outer part of FimA. The genes encoding the structural proteins and the main component were similarly distant from the reference strain in P. gingivalis, but not in P. gulae.

Conclusions

The differences in the gene clusters between P. gingivalis and P. gulae may result in their host specificity.

Identification of Streptococcus cristatus peptides that repress expression of virulence genes in Porphyromonas gingivalis

Dental plaque is a complex multispecies biofilm, and is a direct precursor of periodontal disease. The virulence of periodontal pathogens, such as Porphyromonas gingivalis, is expressed in the context of this polymicrobial community. Previously, we reported an antagonistic relationship between Streptococcus cristatus and P. gingivalis, and identified arginine deiminase (ArcA) of S. cristatus as the signaling molecule to which P. gingivalis responds by repressing the expression and production of FimA protein. Here we demonstrate that direct interaction between P. gingivalis and S. cristatus is necessary for the cell-cell communication. Two surface proteins of P. gingivalis, PGN_0294 and PGN_0806, were found to interact with S. cristatus ArcA. Using a peptide array analysis, we identified several P. gingivalis-binding sites of ArcA, which led to the discovery of an 11-mer peptide with the native sequence of ArcA that repressed expression of fimbriae and of gingipains. These data indicate that a functional motif of ArcA is sufficient to selectively alter virulence gene expression in P. gingivalis, and PGN_0294 and PGN_0806 may serve as receptors for ArcA. Our findings provide a molecular basis for future rational design of agents that interfere with the initiation and formation of a P. gingivalis-induced pathogenic community.

Fimbriae-mediated outer membrane vesicle production and invasion of Porphyromonas gingivalis

Porphyromonas gingivalis is a keystone periopathogen that plays an essential role in the progress of periodontitis. Like other gram-negative bacteria, the ability of P. gingivalis to produce outer membrane vesicles is a strategy used to interact with, and survive within its biological niches. Here we compared the protein components associated with vesicles derived from a fimbriated strain (33277) and an afimbriated strain (W83) of P. gingivalis using proteomic analyses. Some well-known virulence factors were identified in vesicles from both strains, such as gingipains and hemagglutinin. In contrast, FimC, FimD, and FimE, minor components of long fimbriae were found exclusively in 33277 vesicles, while proteins with a tetratricopeptide repeat (TPR) domain were unique to W83 vesicles. We found that significantly more 33277 than W83 vesicles were internalized into human oral keratinocytes and gingival fibroblasts. Interestingly, FimA, a well-known adhesin responsible for the attachment and invasion of P. gingivalis into host cells, was not essential for the invasive capabilities of P. gingivalis vesicles. Rather minor components of long fimbriae were required for an efficient invasive activity of vesicles. The most striking finding was that P. gingivalis strains lacking or having a reduced FimA expression showed a significant reduction in vesiculation. These results suggest that production and pathogenicity of P. gingivalis vesicles may largely depend on expression of the fim locus, and that the integration of vesicle production and pathogenicity with fimbrial expression may allow P. gingivalis to confer upon itself certain functional advantages.

Disruption of heterotypic community development by Porphyromonas gingivalis with small molecule inhibitors

Porphyromonas gingivalis is one of the main etiological organisms in periodontal disease. On oral surfaces P. gingivalis is a component of multispecies biofilm communities and can modify the pathogenic potential of the community as a whole. Accumulation of P. gingivalis in communities is facilitated by interspecies binding and communication with the antecedent colonizer Streptococcus gordonii. In this study we screened a library of small molecules to identify structures that could serve as lead compounds for the development of inhibitors of P. gingivalis community development. Three small molecules were identified that effectively inhibited accumulation of P. gingivalis on a substratum of S. gordonii. The structures of the small molecules are derived from the marine alkaloids oroidin and bromoageliferin and contain a 2-aminoimidazole or 2-aminobenzimidazole moiety. The most active compounds reduced expression of mfa1 and fimA in P. gingivalis, genes encoding the minor and major fimbrial subunits, respectively. These fimbrial adhesins are necessary for P. gingivalis co-adhesion with S. gordonii. These results demonstrate the potential for a small molecular inhibitor-based approach to the prevention of diseases associated with P. gingivalis.

Analysis of Major Virulence Factors inPorphyromonas gingivalisunder Various Culture Temperatures Using Specific Antibodies

Porphyromonas gingivalis is implicated in the occurrence of adult periodontitis. We have previously identified major outer membrane proteins from P. gingivalis, which include representative virulence factors such as gingipains, a 75 kDa major protein, RagA, RagB, and putative porin. Fimbriae, another important virulence factor, exist on the cell surface. In this study, we identified major supernatant proteins. They were fimbrilin, the 75 kDa major protein, gingipains and their adhesin domains. Microscopic examination showed that supernatant proteins formed vesicle-like and fimbrial structures. To learn more about the character of this bacterium, we examined effects of growth temperature on localization and expression of these virulence factors. In general, localization of major virulence factors did not change at the various growth temperatures used. Most of the 75 kDa major protein, RagA, RagB, and putative porin were found in the envelope fraction, not in cell-free culture supernatant. Gingipains were found in both the envelope fraction and supernatant. More than 80% of fimbriae were associated with cells, less than 20% migrated to the supernatant. Most fimbriae existed in the whole cell lysate, although there was a small amount in the envelope fraction. When the growth temperature was increased, expression of fimbriae, gingipains, the 75 kDa major protein, RagA, and RagB decreased. However, temperature had almost no effect on expression of putative porin. The tendency for expression of major virulence factors to decrease at higher temperatures may enable P. gingivalis to survive under hostile conditions.

Porphyromonas gingivalis fimbriae

Marginal periodontitis is not a homogeneous disease but is rather influenced by an intricate set of host susceptibility differences as well as diversities in virulence among the harbored organisms. It is likely that clonal heterogeneity of subpopulations with both high and low levels of pathogenicity exists among organisms harbored by individuals with negligible, slight, or even severe periodontal destruction. Therefore, specific virulent clones of periodontal pathogens may cause advanced and/or aggressive periodontitis. Porphyromonas gingivalis is a predominant periodontal pathogen that expresses a number of potential virulence factors involved in the pathogenesis of periodontitis, and accumulated evidence shows that its expression of heterogenic virulence properties is dependent on clonal diversity. Fimbriae are considered to be critical factors that mediate bacterial interactions with and invasion of host tissues, with P. gingivalis shown to express two distinct fimbria-molecules, long and short fimbriae, on the cell surface, both of which seem to be involved in development of periodontitis. Long fimbriae are classified into six types (I to V and Ib) based on the diversity of fimA genes encoding FimA (a subunit of long fimbriae). Studies of clones with type II fimA have revealed their significantly greater adhesive and invasive capabilities as compared to other fimA type clones. Long and short fimbriae induce various cytokine expressions such as IL-1α, IL-β, IL-6, and TNF-α, which result in alveolar bone resorption. Although the clonal diversity of short fimbriae is unclear, distinct short fimbria-molecules have been found in different strains. These fimbriae variations likely influence the development of periodontal disease.

Microbial interactions in building of communities

Establishment of a community is considered to be essential for microbial growth and survival in the human oral cavity. Biofilm communities have increased resilience to physical forces, antimicrobial agents and nutritional variations. Specific cell-to-cell adherence processes, mediated by adhesin-receptor pairings on respective microbial surfaces, are able to direct community development. These interactions co-localize species in mutually beneficial relationships, such as streptococci, veillonellae, Porphyromonas gingivalis and Candida albicans. In transition from the planktonic mode of growth to a biofilm community, microorganisms undergo major transcriptional and proteomic changes. These occur in response to sensing of diffusible signals, such as autoinducer molecules, and to contact with host tissues or other microbial cells. Underpinning many of these processes are intracellular phosphorylation events that regulate a large number of microbial interactions relevant to community formation and development.

HOG-MAPK signaling regulates the adaptive responses of Aspergillus fumigatus to thermal stress and other related stress

Aspergillus fumigatus is naturally exposed to a highly variable environment and subjected to various kinds of stresses. High-osmolarity glycerol mitogen-activated protein kinase (HOG-MAPK) pathway plays a crucial role in regulating cellular homeostasis in response to environmental changes. Here, we explored the contribution of HOG-MAPK pathway to the adaptive responses to thermal stress and other related stresses in A. fumigatus. We observed the phenotype features of wild-type strains and their derived mutants at 37 and 48 °C, and the results suggested that tcsB participates in response to high temperature. Furthermore, susceptibility test for antifungal drugs showed that SHO1 branch is probably involved in the susceptibility of A. fumigatus to itraconazole at high temperature. Although sakA expression at mRNA level appeared unchanged in wild-type AF293 subjected to thermal stress, phosphorylated SakAp level increased significantly in the strains exposed to cold stress, 250 mmol/L nystatin or 10 % dimethyl sulfoxide in a manner dependent on the SLN1 branch and independent on the SHO1 branch. Taken together, these results indicate that HOG-MAPK pathway, especially the SLN1 branch, plays an important role in the adaptations of A. fumigatus to thermal stress and other related stresses.

A streptococcal effector protein that inhibits Porphyromonas gingivalis biofilm development

Dental plaque formation is a developmental process involving cooperation and competition within a diverse microbial community, approximately 70 % of which is composed of an array of streptococci during the early stages of supragingival plaque formation. In this study, 79 cell-free culture supernatants from a variety of oral streptococci were screened to identify extracellular compounds that inhibit biofilm formation by the oral anaerobe Porphyromonas gingivalis strain 381. The majority of the streptococcal supernatants (61 isolates) resulted in lysis of P. gingivalis cells, and some (17 isolates) had no effect on cell viability, growth or biofilm formation. One strain, however, produced a supernatant that abolished biofilm formation without affecting growth rate. Analysis of this activity led to the discovery that a 48 kDa protein was responsible for the inhibition. Protein sequence identification and enzyme activity assays identified the effector protein as an arginine deiminase. To identify the mechanism(s) by which this protein inhibits biofilm formation, we began by examining the expression levels of genes encoding fimbrial subunits; surface structures known to be involved in biofilm development. Quantitative RT-PCR analysis revealed that exposure of P. gingivalis cells to this protein for 1 h resulted in the downregulation of genes encoding proteins that are the major subunits of two distinct types of thin, single-stranded fimbriae (fimA and mfa1). Furthermore, this downregulation occurred in the absence of arginine deiminase enzymic activity. Hence, our data indicate that P. gingivalis can sense this extracellular protein, produced by an oral streptococcus (Streptococcus intermedius), and respond by downregulating expression of cell-surface appendages required for attachment and biofilm development.

Histidine kinase-mediated production and autoassembly of Porphyromonas gingivalis fimbriae

Porphyromonas gingivalis, a Gram-negative oral anaerobe, is strongly associated with chronic adult periodontitis, and it utilizes FimA fimbriae to persistently colonize and evade host defenses in the periodontal crevice. The FimA-related gene cluster (the fim gene cluster) is positively regulated by the FimS-FimR two-component system. In this study, comparative analyses between fimbriate type strain ATCC 33277 and fimbria-deficient strain W83 revealed differences in their fimS loci, which encode FimS histidine kinase. Using a reciprocal gene exchange system, we established that FimS from W83 is malfunctional. Complementation analysis with chimeric fimS constructs revealed that W83 FimS has a defective kinase domain due to a truncated conserved G3 box motif that provides an ATP-binding pocket. The introduction of the functional fimS from 33277 restored the production, but not polymerization, of endogenous FimA subunits in W83. Further analyses with a fimA-exchanged W83 isogenic strain showed that even the fimbria-deficient W83 retains the ability to polymerize FimA from 33277, indicating the assembly of mature FimA by a primary structure-dependent mechanism. It also was shown that the substantial expression of 33277-type FimA fimbriae in the W83 derivative requires the introduction and expression of the functional 33277 fimS. These findings indicate that FimSR is the unique and universal regulatory system that activates the fim gene cluster in a fimA genotype-independent manner.

FimR and FimS: biofilm formation and gene expression in Porphyromonas gingivalis

Porphyromonas gingivalis is a late-colonizing bacterium of the subgingival dental plaque biofilm associated with periodontitis. Two P. gingivalis genes, fimR and fimS, are predicted to encode a two-component signal transduction system comprising a response regulator (FimR) and a sensor histidine kinase (FimS). In this study, we show that fimS and fimR, although contiguous on the genome, are not part of an operon. We inactivated fimR and fimS in both the afimbriated strain W50 and the fimbriated strain ATCC 33277 and demonstrated that both mutants formed significantly less biofilm than their respective wild-type strains. Quantitative reverse transcription-real-time PCR showed that expression of fimbriation genes was reduced in both the fimS and fimR mutants of strain ATCC 33277. The mutations had no effect, in either strain, on the P. gingivalis growth rate or on the response to hydrogen peroxide or growth at pH 9, at 41 degrees C, or at low hemin availability. Transcriptome analysis using DNA microarrays revealed that inactivation of fimS resulted in the differential expression of 10% of the P. gingivalis genome (>1.5-fold; P < 0.05). Notably genes encoding seven different transcriptional regulators, including the fimR gene and three extracytoplasmic sigma factor genes, were differentially expressed in the fimS mutant.

Anchoring and length regulation of Porphyromonas gingivalis Mfa1 fimbriae by the downstream gene product Mfa2

Porphyromonas gingivalis, a causative agent of periodontitis, has at least two types of thin, single-stranded fimbriae, termed FimA and Mfa1 (according to the names of major subunits), which can be discriminated by filament length and by the size of their major fimbrilin subunits. FimA fimbriae are long filaments that are easily detached from cells, whereas Mfa1 fimbriae are short filaments that are tightly bound to cells. However, a P. gingivalis ATCC 33277-derived mutant deficient in mfa2, a gene downstream of mfa1, produced long filaments (10 times longer than those of the parent), easily detached from the cell surface, similar to FimA fimbriae. Longer Mfa1 fimbriae contributed to stronger autoaggregation of bacterial cells. Complementation of the mutant with the wild-type mfa2 allele in trans restored the parental phenotype. Mfa2 is present in the outer membrane of P. gingivalis, but does not co-purify with the Mfa1 fimbriae. However, co-immunoprecipitation demonstrated that Mfa2 and Mfa1 are associated with each other in whole P. gingivalis cells. Furthermore, immunogold microscopy, including double labelling, confirmed that Mfa2 was located on the cell surface and likely associated with Mfa1 fimbriae. Mfa2 may therefore play a role as an anchor for the Mfa1 fimbriae and also as a regulator of Mfa1 filament length. Two additional downstream genes (pgn0289 and pgn0290) are co-transcribed with mfa1 (pgn0287) and mfa2 (pgn0288), and proteins derived from pgn0289, pgn0290 and pgn0291 appear to be accessory fimbrial components.

Comparative transcriptomic analysis of Porphyromonas gingivalis biofilm and planktonic cells

BACKGROUND

Porphyromonas gingivalis in subgingival dental plaque, as part of a mature biofilm, has been strongly implicated in the onset and progression of chronic periodontitis. In this study using DNA microarray we compared the global gene expression of a P. gingivalis biofilm with that of its planktonic counterpart grown in the same continuous culture.

RESULTS

Approximately 18% (377 genes, at 1.5 fold or more, P-value < 0.01) of the P. gingivalis genome was differentially expressed when the bacterium was grown as a biofilm. Genes that were down-regulated in biofilm cells, relative to planktonic cells, included those involved in cell envelope biogenesis, DNA replication, energy production and biosynthesis of cofactors, prosthetic groups and carriers. A number of genes encoding transport and binding proteins were up-regulated in P. gingivalis biofilm cells. Several genes predicted to encode proteins involved in signal transduction and transcriptional regulation were differentially regulated and may be important in the regulation of biofilm growth.

CONCLUSION

This study analyzing global gene expression provides insight into the adaptive response of P. gingivalis to biofilm growth, in particular showing a down regulation of genes involved in growth and metabolic activity.

Genetic manipulation of Porphyromonas gingivalis

Porphyromonas gingivalis, an oral anaerobic bacterium, is an important etiological agent of periodontal disease and may contribute to cardiovascular disease, preterm birth, and diabetes as well. Therefore, genetic studies are of crucial importance in investigating molecular mechanisms of P. gingivalis virulence. Although molecular genetic tools have been available for many bacterial species for some time, genetic manipulations of Porphyromonas species were not developed until more recently and remain limited. In this unit, current molecular genetic approaches for mutant construction in P. gingivalis using the suicide vector pPR-UF1 and the transposon Tn4351 are described, as are protocols for performing electroporation and conjugation. Furthermore, a technique to restore the wild-type phenotype of the mutant by complementation using vector pT-COW is provided. Finally, a description of a noninvasive reporter system allowing the study of gene expression and regulation in P. gingivalis completes this unit.

Surface components of Porphyromonas gingivalis

BACKGROUND AND OBJECTIVE

Research on Porphyromonas gingivalis, a periodontopathogen, has provided a tremendous amount of information over the last 20 years, which may exceed in part than that on other closely related members in terms of phylogenetic as well as proteomic criteria, including Bacteroides fragilis and B. thetaiotaomicron as major anaerobic, opportunistic pathogens in the medical field. In this minireview, we focused on recent research findings concerning surface components such as outer membrane proteins and fimbriae, of P. gingivalis.

MATERIAL AND METHODS

Elucidation of the surface components in P. gingivalis was especially difficult because outer membrane proteins are tightly bound to lipopolysaccharide and they are resistant to dissociation and separation from each other, even during sodium dodecyl sulfate-polyacrylamide gel electrophoresis, unless samples are appropriately heated. In addition, P. gingivalis is asaccharolytic and therefore a potent proteolytic bacterium, another factor causing difficulty in research. The study of the surface components was carefully carried out considering these unique features in P. gingivalis when compared with other gram-negative bacteria, including Escherichia coli and Pseudomonas aeruginosa.

RESULTS

Separation of outer membrane proteins, and characterization of OmpA-like proteins and RagAB as major proteins, is described herein. Our recent findings on FimA and Mfa1 fimbriae, two unique appendages in this organism, and on their regulation of expression are also described briefly.

CONCLUSION

Surface components of P. gingivalis somehow have contact with host tissues and cells because of the outermost cell elements. Therefore, such bacterial components are potentially important in the occurrence of periodontal diseases.

OxyR is involved in coordinate regulation of expression of fimA and sod genes in Porphyromonas gingivalis

Survival of Porphyromonas gingivalis in the constantly changing oral environment depends on its ability to alter gene expression. We demonstrate here that P. gingivalis activates superoxide dismutase expression in response to oxidative stress and represses expression of FimA, a subunit of major fimbriae. Coordinated expression of fimA and sod is regulated by the redox-sensing transcription factor OxyR. Mutations in the oxyR gene result in a decreased expression of sod and in an elevated expression of fimA. In addition, we provide evidence that regulation of expression of fimA and sod by OxyR is mediated by direct interaction of OxyR and the promoters of these two genes. These results suggest that OxyR plays an important role in regulation of expression of virulence genes in P. gingivalis.

Porphyromonas gingivalis short fimbriae are regulated by a FimS/FimR two-component system

Porphyromonas gingivalis possesses two distinct fimbriae. The long (FimA) fimbriae have been extensively studied. Expression of the fimA gene is tightly controlled by a two-component system (FimS/FimR) through a cascade regulation. The short (Mfa1) fimbriae are less understood. The authors have recently demonstrated that both fimbriae are required for formation of P. gingivalis biofilms. Here, the novel finding that FimR, a member of the two-component regulatory system, is a transcriptional activator of the mfa1 gene is promoted. Unlike the regulatory mechanism of FimA by FimR, this regulation of the mfa1 gene is accomplished by FimR directly binding to the promoter region of mfa1.

Enhanced biofilm formation and loss of capsule synthesis: deletion of a putative glycosyltransferase in Porphyromonas gingivalis

Periodontitis is a biofilm-mediated disease. Porphyromonas gingivalis is an obligate anaerobe consistently associated with severe manifestations of this disease. As an opportunistic pathogen, the ability to proliferate within and disseminate from subgingival biofilm (plaque) is central to its virulence. Here, we report the isolation of a P. gingivalis transposon insertion mutant altered in biofilm development and the reconstruction and characterization of this mutation in three different wild-type strains. The mutation responsible for the altered biofilm phenotype was in a gene with high sequence similarity ( approximately 61%) to a glycosyltransferase gene. The gene is located in a region of the chromosome that includes up to 16 genes predicted to be involved in the synthesis and transport of capsular polysaccharide. The phenotype of the reconstructed mutation in all three wild-type backgrounds is that of enhanced biofilm formation. In addition, in strain W83, a strain that is encapsulated, the glycosyltransferase mutation resulted in a loss of capsule. Further experiments showed that the W83 mutant strain was more hydrophobic and exhibited increased auto-aggregation. Our results indicate that we have identified a gene involved in capsular-polysaccharide synthesis in P. gingivalis and that the production of capsule prevented attachment and the initiation of in vitro biofilm formation on polystyrene microtiter plates.

Two-component signal transduction in human fungal pathogens

Signal transduction pathways provide mechanisms for adaptation to stress conditions. One of the most studied of these pathways is the HOG1 MAP kinase pathway that in Saccharomyces cerevisiae is used to adapt cells to osmostress. The HOG1 MAPK has also been studied in Candida albicans, and more recently observations on the Hog1p functions have been described in two other human pathogens, Aspergillus fumigatus and Cryptococcus neoformans. The important, but not surprising, concept is that this pathway is used for different yet similar functions in each of these fungi, given their need to adapt to different environmental signals. Current studies of C. albicans focus upon the identification of two-component signal proteins that, in both C. albicans and S. cerevisiae, regulate the HOG1 MAPK. In C. albicans, these proteins regulate cell wall biosynthesis (and, therefore, adherence to host cells), osmotic and oxidant adaptation, white-opaque switching, morphogenesis, and virulence of the organism.

A regulation cascade controls expression of Porphyromonas gingivalis fimbriae via the FimR response regulator

Little is known about how Porphyromonas gingivalis, a Gram-negative oral anaerobe, senses environmental changes, and how such information is transmitted to the cell. The production of P. gingivalis surface fimbriae is regulated by FimS-FimR, a two component signal transduction system. Expression of fimA, encoding the fimbrilin protein subunit of fimbriae, is positively regulated by the FimR response regulator. In this study we investigated the molecular mechanisms of FimR regulation of fimA expression. Comparative transcription profiling of fimR wild-type and mutant strains shows that FimR controls the expression of several genes including five clustered around the fimA locus. Chromatin immunoprecipitation assays and electrophoretic mobility shift assays identify and confirm that FimR binds to the promoter region of the first gene in the fimA cluster. Gene expression analyses of mutant strains reveal a transcriptional cascade involving multiple steps, with FimR activating expression of the first gene of the cluster that encodes a key regulatory protein.

A novel type of two-component regulatory system affecting gingipains in Porphyromonas gingivalis

We surveyed the Porphyromonas gingivalis W83 genome database for homologues of FimS, the first two-component sensor histidine kinase, which could possibly control virulence factors. Including fimS, we found six putative sensor kinase genes in the genome. The gene encoding one of the homologues was cloned from a P. gingivalis plasmid library, sequenced, and analyzed using its mutants. Two gene-disruption mutants were created in strain ATCC 33277 by introducing a drug cassette into the gene. The mutants formed nonpigmented colonies, indicating that they might be defective in proteinase production, a characteristic of this organism. Proteinase activities, measured as arginine- and lysine-specific (Rgp and Kgp gingipains, respectively) activities, of the mutants were almost half those of the parent strain. Unlike the parent and wildtype strains, most of the gingipain activities were detected in the culture supernatant, not in cells, of the mutants. Abnormal production of gingipains was confirmed by sodium dodecyl sulfate polyacrylamide gel electrophoresis and Western blot analyses. These results strongly suggest that this newly-discovered two-component sensor kinase is involved in maturation and proper localization of gingipains to the outer membrane through an unknown mechanism. The gene encoding the sensor histidine kinase was designated gppX, which represents regulation (X) of gingipains and black pigmentation in P. gingivalis.

Porphyromonas gingivalis genes involved in fimA regulation

Porphyromonas gingivalis is an important component of the complex plaque biofilm that is a direct precursor of periodontal disease. The major fimbriae are required for attachment to oral surfaces and are an important virulence factor. Fimbrillin (FimA) expression in P. gingivalis is inhibited by surface molecule of Streptococcus cristatus, an early colonizer of dental plaque. In this study, differential display PCR was used to identify P. gingivalis genes that are regulated in response to S. cristatus. Of several differentially expressed genes, pg2131 and pg2167 were upregulated by S. cristatus signaling molecules. A null mutant of pg2167 did not transcriptionally regulate fimA following exposure to S. cristatus. In fact, fimA transcription was enhanced in the pg2167 mutant, suggesting that pg2167 may act to repress fimA expression. In contrast, a mutation in pg2131 did not affect transcription of fimA in the presence of S. cristatus. However, production of fimbrillin was significantly diminished in the pg2131 mutant, implicating involvement in posttranscriptional regulation in fimbriation. These data suggest that P. gingivalis fimbriation is controlled by more than one regulation mechanism, involving both transcriptional and posttranscriptional processes.

Effects of various culture environments on expression of major outer membrane proteins fromPorphyromonas gingivalis

We examined the effects of various culture environments on major outer membrane proteins from Porphyromonas gingivalis ATCC 33277. Major outer membrane protein patterns on gel electrophoresis showed little difference over the culturable range of osmolarity and pH. With elevated temperature or prolonged culture, the intensities of the gingipain bands decreased; however, bands of RagA, RagB and the putative porins were relatively stable. Similar results were observed with several different culture media. Although the precise functions of RagA, RagB and the putative porins are unknown, these factors may be strongly related to the initiation and progression of adult periodontitis.

Transposon-induced norfloxacin-sensitive mutants of Bacteroides thetaiotaomicron

To elucidate the mechanism of norfloxacin (a fluoroquinolone) resistance of Bacteroides thetaiotaomicron, a member of the B. fragilis group, we isolated transposon-induced mutants sensitive to this agent using Tn4351. Four norfloxacin-sensitive mutants showed reduced levels of resistance, at least, to ethidium bromide. Cloning and sequencing of three chromosomal fragments adjacent to Tn4351 from the mutants revealed that two partial open reading frames (orfs) were disrupted by a transposon. Amino acid sequences of partial orf products had strong homologies to those of Escherichia coli RecB and B. ovatus transketolase. Two mutants carried a recB homolog inserted by Tn4351 together with R751 (cointegration) and by itself (simple transposition) at the amino- and carboxyl-terminal portions, respectively. Since mutations in recB produce E. coli cells sensitive to DNA-damaging treatments by quinolones, it is concluded that decreases of the minimum inhibitory concentrations (MICs) of the agents for B. thetaiotaomicron resulted from disruption of the recB homolog. Another mutant carried a transketolase gene inserted by Tn4351. There is no reasonable explanation why disruption of the transketolase gene caused a decrease of the MIC of norfloxacin for this organism, although Streptococcus pneumoniae RecP related to DNA recombination was reported to be transketolase.

Role of the Streptococcus gordonii SspB protein in the development of Porphyromonas gingivalis biofilms on streptococcal substrates

Porphyromonas gingivalis is an aggressive periodontal pathogen that persists in the mixed-species plaque biofilm on tooth surfaces. P. gingivalis cells attach to the plaque commensal Streptococcus gordonii and this coadhesion event leads to the development of P. gingivalis biofilms. Binding of these organisms is multimodal, involving both the P. gingivalis major fimbrial FimA protein and the species-specific interaction of the minor fimbrial Mfa1 protein with the streptococcal SspB protein. This study examined the contribution of the Mfa1-SspB interaction to P. gingivalis biofilm formation. P. gingivalis biofilms readily formed on substrata of S. gordonii DL1 but not on Streptococcus mutans cells which lack a coadhesion-mediating homologue of SspB. An insertional inactivation of the mfa1 gene in P. gingivalis resulted in a phenotype deficient in S. gordonii binding and unable to form biofilms. Furthermore, analysis using recombinant streptococci and enterococci showed that P. gingivalis biofilms formed on Enterococcus faecalis strains expressing SspB or translational fusions of SspB with SpaP (the non-adherent SspB homologue in S. mutans) containing the P. gingivalis adherence domain (SspB adherence region, BAR) of SspB. In contrast, an isogenic Ssp null mutant of S. gordonii DL1 was unable to support biofilm growth, even though this strain bound to P. gingivalis FimA at levels similar to wild-type S. gordonii DL1. Finally, site-specific mutation of two functional amino acid residues in BAR resulted in SspB polypeptides that did not promote the development of P. gingivalis biofilms. These results suggest that the induction of P. gingivalis biofilms on a streptococcal substrate requires functional SspB-minor fimbriae interactions.